RE: [PATCH 3/3] vfio: Report PASID capability via VFIO_DEVICE_FEATURE ioctl

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Monday, November 27, 2023 2:39 PM
> 
> +static int vfio_pci_core_feature_pasid(struct vfio_device *device, u32 flags,
> +				       struct vfio_device_feature_pasid __user
> *arg,
> +				       size_t argsz)
> +{
> +	struct vfio_pci_core_device *vdev =
> +		container_of(device, struct vfio_pci_core_device, vdev);
> +	struct vfio_device_feature_pasid pasid = { 0 };
> +	struct pci_dev *pdev = vdev->pdev;
> +	u32 capabilities = 0;
> +	int ret;
> +
> +	/* We do not support SET of the PASID capability */

this line alone is meaningless. Please explain the reason e.g. due to
no PASID capability per VF...

> +	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
> +				 sizeof(pasid));
> +	if (ret != 1)
> +		return ret;
> +
> +	/*
> +	 * Needs go to PF if the device is VF as VF shares its PF's
> +	 * PASID Capability.
> +	 */

/* VF shares the PASID capability of its PF */

> +	if (pdev->is_virtfn)
> +		pdev = pci_physfn(pdev);
> +
> +	if (!pdev->pasid_enabled)
> +		goto out;
> +
> +#ifdef CONFIG_PCI_PASID
> +	pci_read_config_dword(pdev, pdev->pasid_cap + PCI_PASID_CAP,
> +			      &capabilities);
> +#endif

#ifdef is unnecessary. If CONFIG_PCI_PASID is false pdev->pasid_enabled
won't be set anyway.

and it should read from PCI_PASID_CTRL which indicates whether a
capability is actually enabled.

> +/**
> + * Upon VFIO_DEVICE_FEATURE_GET, return the PASID capability for the
> device.
> + * Zero width means no support for PASID.

also mention the encoding of this field according to PCIe spec.

or turn it to a plain number field.

> + */
> +struct vfio_device_feature_pasid {
> +	__u16 capabilities;
> +#define VFIO_DEVICE_PASID_CAP_EXEC	(1 << 0)
> +#define VFIO_DEVICE_PASID_CAP_PRIV	(1 << 1)
> +	__u8 width;
> +	__u8 __reserved;
> +};
> +#define VFIO_DEVICE_FEATURE_PASID 11
> +
>  /* -------- API for Type1 VFIO IOMMU -------- */
> 
>  /**
> --
> 2.34.1